With advances in computing and communication technology, increasingly devices integrate a number of components to increase their versatility and performance. Many of these components emit electromagnetic noise that can couple into a receiving antenna of the device, degrading radiated sensitivity. Even for devices that exploit unprotected frequency spectra (e.g., WiFi, WiMAX, etc.), degradation in performance can cause customer dissatisfaction and support costs.
Upfront testing costs can be even greater for devices that exploit protected spectra. Total Isotropic Sensitivity (TIS) testing is required to certify any new device for use on commercial networks and is essential to ensure a minimum quality of forward link service. However, TIS testing is a costly and time consuming process that requires formal testing at carrier designated certified labs (e.g., Cellular Telecommunications and Internet Association (CTIA).
Conventionally, a near-field probe can locate the general location within a device that is causing radio frequency (RF) emissions. However, the fact that such RF emissions are occurring does not necessarily mean that these emissions will couple into an antenna of the device or otherwise degrade performance. Consequently, such testing can result in unnecessary modifications before TIS testing or prove to be a time consuming method of troubleshooting after a TIS testing failure.
As an example of devices that are greatly disadvantaged by such certification requirements, notebook vendors routinely offer multiple hardware configurations for the same base model, with different processor speed, drive type, or display type, etc. Each configuration potentially has a different RF emission profile with the possibility of new interference sources in a Wireless Wide Area Network (WWAN) module receiver band or other wireless format. Each configuration necessitates fresh evaluation of radiated sensitivity and this adds significant overhead to the introduction of minor device revisions and configurations. This is a particular if not unique barrier for notebook vendors.
As another example, measuring an embedded wireless device's receiver performance can use a network simulator in a shielded radio frequency environment. A network simulator is used to establish a test call from the emulator to the embedded wireless device using an over-the-air antenna inside an RF shielded chamber. The receiver performance is measured by monitoring errors in the wireless link from the network emulator to the wireless device (e.g., Packet Error Rate, Frame Error Rate, Bit Error Rate, and Symbol Error Rate). The signal level from the network emulator is adjusted until the target wireless link error rate is established. Each time the network emulator is adjusted, the error link measurement cycle requires 300 to 1000 data packets (or frames or bits) to get statistically significant measurement of receiver performance. These methods require expensive network simulators and take a long time to find the target link error rate at multiple channels.
As yet another example, it has been proposed that a spectrum analyzer can be connected to an antenna of an embedded wireless module in a device such as a laptop or notebook computer. The spectrum analyzer can detect a noise profile by scanning the signals received by the antenna. Analyzing the raw data poses certain challenges. Another challenge is testing uncertainties introduced by the invasive nature of testing with a spectrum analyzer. Disassembly to insert a cable to an embedded antenna can violate the integrity of the device, changing characteristics of the device itself, changing a grounding state of the device, and posing impedance matching problems.